Chromium Toxicity and Tolerance in Crop Plants
Heavy metals (HM) constitute a group of pollutants that exert a major influence on the integrity of soil, water and air. Chromium (Cr) is one of these pollutants and its amount has shown a multifold increase in the present era. The role of Cr in plants st
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Chromium Toxicity and Tolerance in Crop Plants Ishrat Khan, Hema Diwan and Altaf Ahmad
1 Introduction Industrialization and technological advancements, the hallmarks of civilization have been increasing heavy metal releases into the environment, that pose a significant threat to environment and public health because of their toxicity, accumulation in the food chain and persistence in nature. Chromium (Cr) is of particular concern as it, when accumulated at high levels, can generate serious trouble and diseases and, as concentration reaches a saturation point, it can become lethal. Within the environment, chromium is found primarily in two oxidation states: Cr(VI) and Cr(III). These two oxidation states of chromium are drastically different in charge, physicochemical properties as well as chemical and biochemical reactivity. Cr(III) results from the weathering of minerals and is the most stable state of environmental chromium. Cr(VI) in the environment is man-made, the result of contamination by industrial emissions (Bartlett 1991; Kotas Stasicka 2000), and is more toxic (EPAUS 1984). Examples of Cr(III) compounds include chromium acetate, chromium chloride, chromic oxide, and chromium sulfate; examples of Cr(VI) compounds include ammonium chromate, calcium chromate, potassium chromate, potassium dichromate, and sodium chromate. Although chromium contamination can originate from natural sources (e.g., in situ weathering of rock minerals can lead to metal contamination in soils), it mainly comes from several industrial and agricultural activities such as ore refining, electroplating, tanning, phosphate fertilizers and waste disposal on land (Shanker et al. 2005). Chromium(VI) is used on a large scale in many different industries, including metallurgical, electroplating, production of paints and pigments, tanning, wood preservation, chromium chemicals production, and pulp and paper production. Often wastes from such industries A. Ahmad () · I. Khan · H. Diwan Molecular Ecology Laboratory, Department of Botany, Faculty of Science, Jamia Hamdard (Hamdard University), New Delhi 110062, India e-mail: [email protected] N. Tuteja, S. S. Gill (eds.), Crop Improvement Under Adverse Conditions, DOI 10.1007/978-1-4614-4633-0_14, © Springer Science+Business Media New York 2013
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(e.g., sludge, fly ash, slag, etc.) are used as a fill material at numerous locations to reclaim marshlands, for tank dikes, and for backfill at sites following demolition (Salunkhe 1998). Cr(VI) from the soils reaches into the groundwater. The tanning industry is especially a large contributor of chromium pollution to water resources; Chandra et al. (1997) estimated that in India alone about 2,000–3,200 tonnes of elemental chromium escapes into the environment annually from the tanning industries, with a chromium concentration ranging between 2,000 and 5,000 mg L−1 in the effluents compared to the recommended permissible limit of 2 mg L−1. Cr(VI) exerts toxic effects on biological systems. It was found that occup
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